Hypertension is a highly prevalent condition which substantially increases the risk of cardiovascular and renal diseases. Lifestyle modifications, including nutrition supplementation, have been suggested as an important means to prevent and treat hypertension. In observational studies, consumption of diets with high fiber content has been associated with a lower blood pressure (BP). However, the few randomized controlled trials that have studied the BP-lowering effect of dietary fiber have produced contradictory results. The overall objective of the proposed study is to test whether dietary fiber supplementation will lower BP in human subjects. The proposed randomized, double-blind, placebo-controlled trial will utilize a prospective parallel design with 200 participants randomly allocated to one of the two treatment arms. The trial is designed to have greater than 80% power to detect a 2 mm Hg reduction in diastolic BP (DBP) and a 3 mm Hg reduction in systolic BP (SBP) over a 6 month intervention. The main eligibility criterion for participation will be a DBP 80 to 89 mm Hg and/or SBP 130 to 139 mm Hg, mean of 9 readings over 3 screening visits. The study participants will be recruited by mass mailing and community-based screening. Following a 2-week run-in period, eligible participants will be randomly allocated to receive either 10 grams of soluble fiber (-glucan extracted from oat bran) per day or placebo. The primary outcome will be change in DBP (defined as the disappearance of the fifth Korotkoff sound) from baseline to termination, with the mean at each of these two points being determined from 9 BP readings (taken over 3 visits). The secondary endpoint will be change in SBP (defined as the appearance of the first Korotkoff sound). In addition, changes in fasting serum glucose, insulin, and total, HDL- and LDL- cholesterol, triglyceride and body weight will be measured, and the impact of these variables on the mechanism of any BP lowering effect will be examined. Results from the proposed study may provide the scientific evidence for new dietary fiber supplementation recommendations for primary prevention of hypertension in the general population.